vii
6 Quality of Service (QoS): Managing Bandwidth More
Effectively
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
QoS Types for Prioritizing Outbound Packets . . . . . . . . . . . . . . . . . . . 6-8
Packet Types and Evaluation Order . . . . . . . . . . . . . . . . . . . . . . . . 6-9
Preparation for Configuring QoS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
Steps for Configuring QoS on the Switch . . . . . . . . . . . . . . . . . . . 6-11
Planning a QoS Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13
Prioritizing and Monitoring QoS Configuration Options . . . . . . 6-13
Using QoS Types To Configure QoS for Outbound Traffic . . . . . . . . . . . . 6-14
Viewing the QoS Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14
No Override . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
QoS IP Type-of-Service (ToS) Policy and Priority . . . . . . . . . . . . . . . 6-16
Assigning an 802.1p Priority to IPv4 Packets on the Basis
of the ToS Precedence Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17
Assigning an 802.1p Priority to IPv4 Packets on the Basis
of Incoming DSCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18
Assigning a DSCP Policy on the Basis of the DSCP in IPv4
Packets Received from Upstream Devices . . . . . . . . . . . . . . . . . . 6-22
Details of QoS IP Type-of-Service . . . . . . . . . . . . . . . . . . . . . . . . . 6-26
QoS Interface (Source-Port) Priority . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29
Assigning a Priority Based on Source-Port . . . . . . . . . . . . . . . . . . 6-29
Differentiated Services Codepoint (DSCP) Mapping . . . . . . . . . . . . . 6-32
Default Priority Settings for Selected Codepoints . . . . . . . . . . . . 6-33
Quickly Listing Non-Default Codepoint Settings . . . . . . . . . . . . . 6-34
Note On Changing a Priority Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-35
IP Multicast (IGMP) Interaction with QoS . . . . . . . . . . . . . . . . . . . . . . . . . 6-36
QoS Messages in the CLI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-36
QoS Operating Notes and Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-37
